Skip to main content Accessibility help
×
  1. Home
  2. Publications
  3. Textbooks
  4. Content Listing

Refine search

Refine search

Access:
Content type:
Publication date:
Apply   From and To filters
Subject: Show more
Journals Show more
Publishers: Show more
Societies Show more
Series: Show more
Collections: Show more

Actions for selected content:

Select all | Deselect all
  • View selected items
  • Export citations
  • Download PDF (zip)
  • Save to Kindle
  • Save to Dropbox
  • Save to Google Drive

Save Search

You can save your searches here and later view and run them again in "My saved searches".

Please provide a title, maximum of 40 characters.
Cancel
×

38612 results in Cambridge Textbooks

Page 1287 of 1931

  • I - Constants, A Programming Module

  • Bradley W. Carroll, Weber State University, Utah, Dale A. Ostlie, Weber State University, Utah
  • Book:
    An Introduction to Modern Astrophysics
    Published online:
    16 August 2019
    Print publication:
    07 September 2017, pp 1294-1294

  • Summary

    Constants is a Fortran 95 module implementation of the astronomical and physical constants data given in Appendix A (a C++ header file version is also available). Constants also includes high-precision values of mathematical constants (π, e) and conversion factors between degrees and radians. In addition, Constants provides various machine constants characteristic of the particular platform that a code is running on. For example, in the Fortran 95 implementation, Constants includes machine-queried KIND designations for single, double, and quadruple precision, the smallest and largest numbers that can be represented by the computer for a specific precision, and the number of significant figures that can be represented for each level of precision.

    Constants is employed by the other codes described in the appendices that follow. The source code is available for download from the resources tab on following

  • 5 - The Interaction of Light and Matter

  • from I - THE TOOLS OF ASTRONOMY
  • Bradley W. Carroll, Weber State University, Utah, Dale A. Ostlie, Weber State University, Utah
  • Book:
    An Introduction to Modern Astrophysics
    Published online:
    16 August 2019
    Print publication:
    07 September 2017, pp 111-140

  • Summary

    SPECTRAL LINES

    In 1835 a French philosopher, Auguste Comte (1798–1857), considered the limits of human knowledge. In his book Positive Philosophy, Comte wrote of the stars, “We see how we may determine their forms, their distances, their bulk, their motions, but we can never know anything of their chemical or mineralogical structure.” Thirty-three years earlier, however, WilliamWollaston (1766–1828), like Newton before him, passed sunlight through a prism to produce a rainbow-like spectrum. He discovered that a number of dark spectral lines were superimposed on the continuous spectrum where the Sun's light had been absorbed at certain discrete wavelengths. By 1814, the German optician Joseph von Fraunhofer (1787–1826) had cataloged 475 of these dark lines (today called Fraunhofer lines) in the solar spectrum. While measuring the wavelengths of these lines, Fraunhofer made the first observation capable of proving Comte wrong. Fraunhofer determined that the wavelength of one prominent dark line in the Sun's spectrum corresponds to the wavelength of the yellow light emitted when salt is sprinkled in a flame. The new science of spectroscopy was born with the identification of this sodium line.

    Kirchhoff's Laws

    The foundations of spectroscopy were established by Robert Bunsen (1811–1899), a German chemist, and by Gustav Kirchhoff (1824–1887), a Prussian theoretical physicist. Bunsen's burner produced a colorless flame that was ideal for studying the spectra of heated substances. He and Kirchhoff then designed a spectroscope that passed the light of a flame spectrum through a prism to be analyzed. The wavelengths of light absorbed and emitted by an element were found to be the same; Kirchhoff determined that 70 dark lines in the solar spectrum correspond to 70 bright lines emitted by iron vapor. In 1860 Kirchhoff and Bunsen published their classic work Chemical Analysis by Spectral Observations, in which they developed the idea that every element produces its own pattern of spectral lines and thus may be identified by its unique spectral line “fingerprint.” Kirchhoff summarized the production of spectral lines in three laws, which are now known as Kirchhoff's laws:

  • • A hot, dense gas or hot solid object produces a continuous spectrum with no dark spectral lines.

  • • A hot, diffuse gas produces bright spectral lines (emission lines).

  • • Acool, diffuse gas in front of a source of a continuous spectrum produces dark spectral lines (absorption lines) in the continuous spectrum.

  • 24 - The Milky Way Galaxy

  • from IV - GALAXIES AND THE UNIVERSE
  • Bradley W. Carroll, Weber State University, Utah, Dale A. Ostlie, Weber State University, Utah
  • Book:
    An Introduction to Modern Astrophysics
    Published online:
    16 August 2019
    Print publication:
    07 September 2017, pp 874-939

  • Summary

    COUNTING THE STARS IN THE SKY

    As we learned in the first two chapters of this text, human beings have long looked up at the heavens and contemplated its vastness, proposing various models to explain its form. In some civilizations the stars were believed to be located on a celestial sphere that rotated majestically above a fixed, central Earth.WhenGalileo made his first telescopic observations of the night sky in 1610, we started down a long road that has dramatically expanded our view of the universe.

    In this chapter we will explore the complex system of stars, dust, gas, and dark matter known as the Milky Way Galaxy. Although it is possible to get at least a general idea about the nature of other galaxies from our external viewpoint, studying our own Galaxy has proved to be very challenging. As we will learn, we live in a disk of stars, dust, and gas that severely impacts our ability to “see” beyond our relative stellar neighborhood when we look along the plane of the disk. The problem is most severe when looking toward the center of the Galaxy in the constellation Sagittarius. In Section 24.1 we will discover that studying the distribution of stars while considering the effects of extinction provides us with our first hint of what the MilkyWay looks like from an outside perspective. In Section 24.2, a detailed description of the many varying components of the Galaxy will be presented.

    Much of what we know today about the formation and evolution of the Milky Way is encoded in the motions of the Galaxy's constituents, especially when combined with information about variations in composition. Unfortunately, measuring the motions of the stars and gas in the Galaxy is done from an observing platform (Earth) that is itself undergoing a complex motion that involves the orbit of Earth around the Sun and the Sun's elaborate path around the Galaxy. In Section 24.3 we will investigate these motions, allowing us to move from a description of motions relative to the Sun to motions relative to the center of the Galaxy.

  • 2 - Celestial Mechanics

  • from I - THE TOOLS OF ASTRONOMY
  • Bradley W. Carroll, Weber State University, Utah, Dale A. Ostlie, Weber State University, Utah
  • Book:
    An Introduction to Modern Astrophysics
    Published online:
    16 August 2019
    Print publication:
    07 September 2017, pp 23-56

  • Summary

    ELLIPTICAL ORBITS

    Although the inherent simplicity of the Copernican model was aesthetically pleasing, the idea of a heliocentric universe was not immediately accepted; it lacked the support of observations capable of unambiguously demonstrating that a geocentric model was wrong.

    Tycho Brahe: The Great Naked-Eye Observer

    After the death of Copernicus, Tycho Brahe (1546–1601), the foremost naked-eye observer, carefully followed the motions of the “wandering stars” and other celestial objects. He carried out his work at the observatory, Uraniborg, on the island of Hveen (a facility provided for him by King Frederick II of Denmark). To improve the accuracy of his observations, Tycho used large measuring instruments, such as the quadrant depicted in the mural in Fig. 2.1(a).Tycho's observations were so meticulous that he was able to measure the position of an object in the heavens to an accuracy of better than 4_, approximately one-eighth the angular diameter of a full moon. Through the accuracy of his observations he demonstrated for the first time that comets must be much farther away than the Moon, rather than being some form of atmospheric phenomenon.Tycho is also credited with observing the supernova of 1572, which clearly demonstrated that the heavens were not unchanging as Church doctrine held. (This observation prompted King Frederick to build Uraniborg.) Despite the great care with which he carried out his work, Tycho was not able to find any clear evidence of the motion of Earth through the heavens, and he therefore concluded that the Copernican model must be false (see Section 3.1).

    Kepler's Laws of Planetary Motion

    At Tycho's invitation, Johannes Kepler (1571–1630), a German mathematician, joined him later in Prague [Fig. 2.1(b)]. Unlike Tycho, Kepler was a heliocentrist, and it was his desire to find a geometrical model of the universe that would be consistent with the best observations then available, namely Tycho's. After Tycho's death, Kepler inherited the massof observations accumulated over the years and began a painstaking analysis of the data. His initial, almost mystic, idea was that the universe is arranged with five perfect solids, nested to support the six known naked-eye planets (including Earth) on crystalline spheres, with the entire system centered on the Sun. After this model proved unsuccessful, he attempted to devise an accurate set of circular planetary orbits about the Sun, focusing specifically on Mars.

  • 12 - The Interstellar Medium and Star Formation

  • from II - THE NATURE OF STARS
  • Bradley W. Carroll, Weber State University, Utah, Dale A. Ostlie, Weber State University, Utah
  • Book:
    An Introduction to Modern Astrophysics
    Published online:
    16 August 2019
    Print publication:
    07 September 2017, pp 398-445

  • Summary

    INTERSTELLAR DUST AND GAS

    When we look into the heavens, it appears as though the stars are unchanging, point-like sources of light that shine steadily. On casual inspection, even our own Sun appears constant. But, as we have seen in the last chapter, this is not the case; sunspots come and go, flares erupt, significant amounts of matter are launched into space via coronal mass ejections, the corona itself changes shape, and even the Sun's luminosity appears to be fluctuating over human timescales, as evidenced by the Maunder minimum. Of course, over the 4.57- Gyr lifetime of our Sun, the luminosity, effective temperature, and radius have all changed substantially (recall Fig. 11.1).

    In fact all stars change. Usually the changes are so gradual and over such long time intervals when measured in human terms that we do not notice them without very careful telescopic observation. Occasionally, however, the changes are extremely rapid and dramatic, as in the case of a supernova explosion. By invoking the understanding we developed thus far of the physics of stellar interiors and atmospheres, we can now begin to examine the processes governing how stars evolve during their lives.

    The Interstellar Medium

    In some sense the evolution of stars is a cyclic process. A star is born out of gas and dust that exists between the stars, known as the interstellar medium (ISM). During its lifetime, depending on the star's total mass, much of that material may be returned to the ISM through stellar winds and explosive events. Subsequent generations of stars can then form from this processed material. As a result, to understand the evolution of a star, it is important to study the nature of the ISM.

    Understanding the interstellar medium is critical for more than its role in stellar evolution, however. The ISM is of profound importance in describing the structure, dynamics, and evolution of our MilkyWay Galaxy, as well as galaxies throughout the universe. In addition, it impacts our observations of everything from relatively nearby stars to the most remote galaxies and quasars.

  • 10 - The Interiors of Stars

  • from II - THE NATURE OF STARS
  • Bradley W. Carroll, Weber State University, Utah, Dale A. Ostlie, Weber State University, Utah
  • Book:
    An Introduction to Modern Astrophysics
    Published online:
    16 August 2019
    Print publication:
    07 September 2017, pp 284-348

  • Summary

    HYDROSTATIC EQUILIBRIUM

    In the last two chapters, many of the observational details of stellar spectra were discussed, along with the basic physical principles behind the production of the observed lines.Analysis of that light, collected by ground-based and space-based telescopes, enables astronomers to determine a variety of quantities related to the outer layers of stars, such as effective temperature, luminosity, and composition. However, with the exceptions of the ongoing detection of neutrinos from the Sun (which will be discussed later in this chapter and in Chapter 11) and the one-time detection from Supernova 1987A (Section 15.3), no direct way exists to observe the central regions of stars.

    Determining the Internal Structures of Stars

    To deduce the detailed internal structure of stars requires the generation of computer models that are consistent with all known physical laws and that ultimately agree with observable surface features. Although much of the theoretical foundation of stellar structure was understood by the first half of the twentieth century, it wasn't until the 1960s that sufficiently fast computing machines became available to carry out all of the necessary calculations. Arguably one of the greatest successes of theoretical astrophysics has been the detailed computer modeling of stellar structure and evolution. However, despite all of the successes of such calculations, numerous questions remain unanswered. The solution to many of these problems requires a more detailed theoretical understanding of the physical processes in operation in the interiors of stars, combined with even greater computational power.

    The theoretical study of stellar structure, coupled with observational data, clearly shows that stars are dynamic objects, usually changing at an imperceptibly slow rate by human standards, although they can sometimes change in very rapid and dramatic ways, such as during a supernova explosion. That such changes must occur can be seen by simply considering the observed energy output of a star. In the Sun, 3.839 × 1026 J of energy is emitted every second. This rate of energy output would be sufficient to melt a 0◦C block of ice measuring 1 AU × 1 mile × 1 mile in only 0.3 s, assuming that the absorption of the energy was 100% efficient. Because stars do not have infinite supplies of energy, they must eventually use up their reserves and die. Stellar evolution is the result of a constant fight against the relentless pull of gravity.

Page 1287 of 1931